The present invention relates to apparatus and methods for pumping, oxygenating and filtering blood having means for removing air or other gasses from the blood.
Each year hundreds of thousands of people are afflicted with vascular diseases, such as arteriosclerosis, that result in cardiac ischemia. For more than thirty years, such disease, especially of the coronary arteries, has been treated using open surgical procedures, such as coronary artery bypass grafting. During such bypass grafting procedures, a sternotomy is performed to gain access to the pericardial sac, the patient is put on cardiopulmonary bypass, and the heart is stopped using a cardioplegia solution.
The development of minimally invasive techniques for cardiac bypass grafting, for example, by Heartport, Inc., Redwood City, Calif., and CardioThoracic Systems, Inc., Menlo Park, Calif., have placed a premium on reducing the size of equipment employed in the sterile field. Whereas open surgical techniques typically provide a relatively large surgical site that the surgeon views directly, minimally invasive techniques require the placement of endoscopes, video monitors, and various positioning systems for the instruments. These devices crowd the sterile field and can limit the surgeon""s ability to maneuver.
At the same time, however, the need to reduce priming volume of the oxygenator and pump, and the desire to reduce blood contact with non-native surfaces has increased interest in locating the oxygenator and pump as near as possible to the patient.
In recognition of the foregoing issues, some previously known cardiopulmonary systems have attempted to miniaturize and integrate certain components of cardiopulmonary systems. U.S. Pat. Nos. 5,266,265 and 5,270,005, both to Raible, describe an extracorporeal blood oxygenation system having an integrated blood reservoir, an oxygenator formed from a static array of hollow fibers, a heat exchanger, a pump and a pump motor that is controlled by cable connected to a control console.
One drawback of systems of the type described in foregoing patents, however, arises during priming of the extracorporeal circuit, and in particular, in the need to use large quantities of saline or donor blood to prime the systems. Such fluids are required to flush air out of the system and, because they are relatively incompressible, ensure that the pump used in the extracorporeal circuit develops sufficient pressure head to propel oxygenated blood back to the patient.
In view of this limitation of previously known blood handling systems, it would be desirable to provide a blood handling system and methods that automatically remove air from an extracorporeal blood circuit.
It further would be desirable to blood handling systems and methods that permit one or more additional blood processing components, such as a heat exchanger, to be added to an extracorporeal blood circuit without having to prime the component prior to bringing that component online, thereby reducing disruption to operation of the blood handling system.
It also would be desirable to provide an extracorporeal blood handling system and methods wherein the blood handling system has compact size and low surface area, and reduces contact between the blood and foreign surfaces, thus reducing priming volume, hemolysis and platelet activation.
It still further would be desirable to provide a blood handling system and methods that provide progressive filtration of blood passing through the system, thus reducing the risk that a single blood filter element will become clogged during extended operation.
In view of the foregoing, it is an object of the present invention to provide apparatus and methods for handling blood that automatically remove air from an extracorporeal blood circuit.
It is another object of the present invention to provide a blood handling system and methods that permit one or more blood processing components, such as a heat exchanger, to be added to an extracorporeal blood circuit without having to prime the component prior to bringing that component online, thereby reducing disruption to operation of the blood handling system.
It is yet another object of this invention to provide an extracorporeal blood handling system and methods wherein the blood handling system has compact size and low surface area, and reduces contact between the blood and foreign surfaces, thus reducing priming volume, hemolysis and platelet activation.
It is a further object of the present invention to provide a blood handling system and methods that provide progressive filtration of blood passing through the system, thus reducing the risk that a single blood filter element will become clogged during extended operation.
These and other objects of the present invention are accomplished by providing a blood handling system comprising an integrated blood oxygenator and pump system having means for removing air or other gases from the extracorporeal blood circuit. In accordance with the principles of the present invention, the blood handling system includes a gas collection plenum, a line adapted to be connected to a suction source, and a sensor that controls coupling of the suction source to the gas collection plenum to selectively remove gas from the blood handling system. The blood handling system of the present invention therefore may be initially primed with little or no saline or donor blood, and with reduced risk of hemodilution.
Moreover, additional components may be added to an existing extracorporeal circuit with little or no additional priming, and any air or other gases introduced into the system will be evacuated with no substantial impact on operation of the blood pump of the blood handling system.
In a preferred embodiment, a blood handling system of the present invention maintains total or partial bypass support for a patient and comprises a housing having a blood inlet, a blood outlet, a gas collection plenum, a blood oxygenation element, a blood pump and a gas removal system.
Blood entering the housing via the blood inlet flows through the gas collection plenum and a first blood filter component that forms part of the gas removal system. Air or other gases entrained in the blood are separated from the blood and collect in the gas collection plenum. A sensor disposed in communication with the gas collection plenum senses a parameter indicative of a level or volume of gas collected in the plenum, and selectively evacuates the plenum by coupling the plenum to a suction source, such as a standard operating room suction port.
Blood exiting the first blood filter component passes to a centrifugal blood pump, which propels the blood through the blood oxygenation element. The blood oxygenation element preferably comprises an annular fiber bundle, e.g., an annular bundle of hollow gas exchange tubes, positioned within the housing. In accordance with another aspect of the present invention, the annular filter bundle serves as a second blood filtration element.
Blood exiting the blood oxygenation element then passes through an additional blood filter element before exiting from the housing through the blood outlet. Blood processed through the system therefore passes through multiple blood filters, which may be progressively finer, distributed throughout the housing, thereby reducing the risk that any one of the filters will be overburdened and clog during extended use of the system.
In still another aspect of the invention, the blood oxygenation element receives blood from the blood pump on a side of the annular fiber bundle that is diametrically opposite to the blood outlet. The inlet to the annular fiber bundle preferably includes an inlet manifold and the blood outlet of the housing preferably has an outlet manifold. The inlet and outlet manifolds preferably extend longitudinally along diametrically opposite sides of the blood oxygenation element, so that blood flows from one side to the diametrically opposite side of the blood oxygenation element.
In a preferred embodiment, the gas removal system includes a gas removal/blood filter element having a cylindrical shape. The gas removal/blood filter comprises a support structure that supports a screen-like material having an effective pore size between 40 and 250 microns. Alternatively, the gas removal/blood filter element may comprise a pleated filter material. Blood is introduced into the gas collection plenum via the blood inlet in a direction substantially tangential to the gas removal/blood filter, to increase residence time of the blood within the gas collection plenum, thereby enhancing separation of entrained gas.
In still another aspect of the present invention, the housing of blood oxygenation element includes at least one relief area positioned radially inward from the annular fiber bundle. More preferably, a relief area is positioned radially inward from each of the inlet and outlet manifolds to permit expansion of the annular fiber bundle at these locations, and to increase the porosity of the fibers in the manifold area and decrease resistance to flow.
Methods of operating the blood handling system of the present invention also are provided.